Yemen rebels who hijacked an Israeli-linked cargo ship in the Red Sea were backed, supported and potentially trained by Iranian authorities, according to a U.S. official.

New photos of the helicopter-borne Houthi attack on the Galaxy Leader, a cargo vessel linked to Israeli billionaire Abraham "Rami" Ungar, shows "all the signs" that Iran was behind the operation, an American defense official told The Associated Press on condition of anonymity.

"This has all the signs these people were trained by a professional military, which could clearly be Iran," the defense official said. "This looks like something we haven’t seen before."

On Sunday, the Yemen rebel group seized the ship as it was traveling from Turkey to India. The rebels, carrying rifles and dressed in commando-style bulletproof vests, covered each other and moved in military formation before they quickly seized control of the bridge of the Galaxy Leader. The Israel Defense Forces described the hijacking as "a very grave incident of global consequence."

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People with guns on the ship

This photo released by the Houthi Media Center shows Houthi forces boarding the cargo ship Galaxy Leader on Sunday, Nov. 19, 2023. Yemen's Houthis seized the ship in the Red Sea off the coast of Yemen after threatening to seize all vessels owned by Israeli companies. (Houthi Media Center via AP)

The hijacking on one of the world’s key shipping routes comes as the Israel-Hamas war continues into its second month. The war started when Hamas, whose chief sponsor is Iran, carried out the deadliest terror attack on Israeli soil on Oct. 7 — killing 1,200 civilians. Yemen's Houthis have threatened to seize all vessels owned by Israeli companies. 

Immediately after the hijacking, Israel suspected Iran was behind the operation.

Rebel fighter with a gun

This photo released by the Houthi Media Center shows Houthi forces boarding the cargo ship Galaxy Leader on Sunday, Nov. 19, 2023. Yemen's Houthis seized the ship in the Red Sea off the coast of Yemen after threatening to seize all vessels owned by Israeli companies. (Houthi Media Center via AP)

Israeli Prime Minister Benjamin Netanyahu’s office said it "strongly condemns the Iranian attack against an international vessel."

"The ship, which is owned by a British company and is operated by a Japanese firm, was hijacked with Iran guidance by the Yemenite Houthi militia," Netanyahu's office continued. "Onboard the vessel are 25 crew members of various nationalities, including Ukrainian, Bulgarian, Filipino and Mexican. No Israelis are onboard. This is another act of Iranian terrorism and constitutes a leap forward in Iran's aggression against the citizens of the free world, with international consequences regarding the security of the global shipping lanes."

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Others are also suspecting Iranian involvement.

The cargo ship

This photo released by the Houthi Media Center shows a Houthi forces helicopter approaching the cargo ship Galaxy Leader on Sunday, Nov. 19, 2023. Yemen's Houthis seized the ship in the Red Sea off the coast of Yemen after threatening to seize all vessels owned by Israeli companies. (Houthi Media Center via AP)

RANE, a risk intelligence firm, said the Houthis displayed tactics reminiscent of those used by Iran's paramilitary Revolutionary Guard when seizing vessels in the past.

Ambrey, a private intelligence firm, similarly said the rebel group had a "sophistication" and referred to the operation as an "Iranian-style vessel seizure" that "provides the Houthis with a negotiation lever" in much the same way Hamas' taking of some 240 hostages in their Oct. 7 attack on Israel did.

"The incident displayed a significant increase in the Houthis' capability to disrupt merchant shipping," Ambrey said. "In the past, the Houthis had only used sea mines, missiles and remote-controlled improvised explosive devices in the Red Sea."

It added, "The sophistication of the operation suggests that Iranian involvement is highly likely."

Helicopter approaching the vessel

This photo released by the Houthi Media Center shows a Houthi forces helicopter approaching the cargo ship Galaxy Leader on Sunday, Nov. 19, 2023. Yemen's Houthis seized the ship in the Red Sea off the coast of Yemen after threatening to seize all vessels owned by Israeli companies. (Houthi Media Center via AP)

Iran has denied any involvement with the attacks. It also previously denied Hamas’ invasion of Israel.

"Those accusations are void, and a result of the complicated situation the Zionist regime is struggling with," Iranian Foreign Ministry spokesman Nasser Kanaani said Monday. "We have said many times that resistance groups in the region represent their own countries and people, and they make decisions based on the interests of their own countries and nations."

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Other Iranian-backed groups, including the Lebanese Shiite militia Hezbollah and Syria fighters, have also engaged in cross-border fire for weeks with Israel.

The Houthi rebel group has displayed weapon sophistication that could suggest other military capabilities.

The Houthis flew a Soviet-era MiG-29 fighter jet over the capital, Sanaa, during a military parade this year, along with a Northrop F-5 Tiger combat aircraft at another. A Houthi parade also saw Soviet-era Mil Mi-17 helicopters flying through the sky — the same helicopter used in Sunday's attack.

A photo of the ship before the attack

This photo released by the Houthi Media Center shows Houthi escorting the cargo ship Galaxy Leader on Sunday, Nov. 19, 2023. Yemen's Houthis seized the ship in the Red Sea off the coast of Yemen after threatening to seize all vessels owned by Israeli companies.  (Houthi Media Center via AP)

The Houthis also have shot down an American MQ-9 Reaper drone during the Israel-Hamas war with a surface-to-air missile, and have fired drones and missiles toward Israel.

The Israeli-Hamas violence now expanding into the Red Sea, which stretches from Egypt's Suez Canal down to the Bab el-Mandeb Strait separating East Africa from the Arabian Peninsula, increases concerns of a wider conflict.

"Significant Houthi interference with commercial shipping through the Strait is almost certain to trigger U.S. intervention due to the political and potentially economic implications," the New York-based Soufan Center warned.

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The U.S. has sent more vessels into and through the Red Sea, including USS Dwight D. Eisenhower and its strike group, in an attempt to deter such an outbreak.

The Galaxy Leader is Japanese-operated and Bahamian-flagged.

Fox News’ Danielle Wallace and The Associated Press contributed to this report.